A number of containers having hinged or otherwise collapsible sidewalls have been proposed, since collapsing sidewalls provides the ability to reduce the volume required for such containers during storage or initial shipment and, for reusable containers, during return-shipment. Containers of this type, however, have often been subject to certain problems or deficiencies. In some configurations, there has been a tendency of the containers to experience a vertical downward deflection near the center of the sidewalls (or base) or "sag" over time. This has been especially pronounced in certain configurations designed for stacking containers vertically one on top of the other. Such sag makes it difficult to efficiently pack containers into a limited space and contributes to material fatigue, eventually leading to failure of the container. Some previous devices have attempted to diminish the sag effect by adding reinforcing beams across the lower surface of the container. However, such beams have often interfered with providing the capability of four-way forklift entry since such beams typically run transverse to the path of forks of a forklift along at least one direction of entry.
Another troublesome type of deflection has been outward sidewall deflection. Use of the containers to transport dense loads results in outward forces being applied to the sidewalls and some amount of deflection often results. This deflection interferes with efficient packing of containers into a confined space. In some applications, containers are designed so that an integral number can be efficiently, (i.e., tightly, with no wasted space) packed into a larger vessel such as the hold of a cargo ship, a trailer, an airplane, etc. However, if the sidewalls of such containers have experienced deflection and, for example, undergone "ballooning," such containers will no longer pack correctly into such defined spaces. Furthermore, if containers are subject to sidewall deflection, even if containers have been successfully packed into a larger vessel, if sidewall deflection occurs after such packing, the containers may become tightly jammed into the larger vessel and it may be difficult to extract such jammed vessels.
In some instances, containers are provided with a removable top or lid, e.g., to protect the contents of the container during shipment, storage, etc. Previous lid devices have often been incompatible with container stacking such that containers were designed to stack in an unlidded condition, or to stack in a lidded condition, but not both. Previous lids with a stacking capability were sometimes susceptible to formation of pools if subjected to water, such as rainwater. Many previous lids added a significant amount of height to the container, particularly if the lids were configured to accommodate stacking. A number of lid designs were useful for storage but were subject to accidental loss during shipment, e.g., by the force of wind acting on the lids.
In some cases, it is desirable to provide one or more doors within one of the collapsible sidewalls to facilitate removal of the container contents. Previously, it has been difficult to successfully locate a door in the lower portion of a sidewall which is designed to swing outward and upward. The design was particularly difficult when the container was intended for bulk transport (i.e., transport of a large number of discrete and loose or unrestrained items, e.g., loose bolts, washers, etc.). In this application, a large amount of force is applied to the door and it has been difficult to design such a door that will successfully withstand the force without failure or undue deflection.
Previous devices have also been subject to deflection of the bottom surface or floor of the container. Some previous designs have provided for ribbing extending downward from the flat floor surface of the container. However, previous devices have required an excessive amount of ribbing to achieve acceptable strength and stiffness contributing to additional weight and cost of the container.